1. Field of the Invention
The present invention relates to dope dyeing in black of polyester fibers, more particularly, black liquid colorants for the dope dyeing of polyester fibers, which have high carbon black contents, are little liable to deteriorate the polyester fibers and can minimize a reddish tone characteristic of carbon blacks, and to polyester fibers dope-dyed with the black liquid colorants.
2. Related Art Statement
Dope-dyed black polyester fibers have been manufactured by the addition of carbon black during polymerization of polyesters or at any steps from polymerization to fiber-formation. The obtained black polyester fibers have been extensively used for manufacturing fabrics to make up, for example, school-uniforms, etc.
However, the dope-dyed black polyester fibers obtained by direct addition of carbon blacks and fabrics made thereof have been considerably reddish as compared with those post-dyed with black dyes. Moreover, they have had drawbacks that the carbon blacks they contain have insufficient dispersibilities and numerous coarse particles are therefore observed in the obtained black polyester fibers. Those coarse particles that are liable to cause filter cloggings, filament breakages, etc. in the spinning step are considered to be attributed to agglomeration of the carbon blacks during the manufacture of polyester fibers, or poor wettabilities of the carbon blacks with polyester resins. In order to eliminate the reddish tone and prevent the agglomeration, there have so far been proposed a combined use of copper phthalocyanine green (Japanese Patent Application Laid-open No. 49-87,792) and a combined use of copper phthalocyanine blue (Japanese Patent Application Publication No. 35,835/78). However, polyester fibers obtained by these proposed processes have not yet had a satisfactory shade and still exhibit an appreciably reddish or yellowish tone.
Further, the dope dyeing processes wherein carbon blacks are directly added during the polyester polymerization, have disadvantages such that heavy staining of polymerization tanks necessitates installation of additional tanks for exclusive use in the process, as well as time- and labor-consuming cleaning work.
As a dope dyeing process to eliminate the above disadvantages, there have been known processes using precolored pellets and color concentrates the precolored pellet processes have scarcely been put into practice due to high cost, technical difficulties such as deterioration of resin, etc.
The processes which utilize color concentrates comprising a polyester resin and a high concentration of pigments or dyes dispersed therein have also various shortcomings. Namely,
(1) technical difficulties are encountered in dispersing a high concentration of pigments or dyes during the manufacture of the color concentrates, PA0 (2) drying of the resin prior to the preparation of the color concentrates, crystallization of the color concentrate after the preparation and, in addition, further occasional drying after the preparation are required, so that energy consumption goes up in the manufacture of the color concentrates, PA0 (3) since the polyester resins to be used for manufacturing the color concentrates have a thermal history of at least two heatings including a thermal history at the time of molding, the inherent viscosity (IV) of the molded products is lowered, and PA0 (4) the necessity to dry the color concentrates when molded, will require the installation of an exclusive drying equipment for color concentrates, or drying of a mixture of natural resin with color concentrate in a drying machine, which makes color changeovers difficult to be dealt with.
As a colorant to eliminate such difficulties in the dope dyeing by color concentrate of polyester fibers, liquid colorants wherein a certain kind of liquid polyester is used as a dispersion medium have been proposed in Japanese Patent Application Laid-open No. 60-45,689. Notwithstanding the liquid colorants have many advantages as a colorant for polyester fibers, some problems remain unsolved when the liquid colorants are practically used in the dyeing of the polyester fibers. That is, in the case of liquid colorants, low carbon black contents in the polyester fibers are caused, because the volume of the colorant to be added to the polyester is restricted due to slippage of the molten polymer mass which increases with the volume of the added liquid colorant in extruders or mixers and further a large oil absorption of the carbon black itself lowers the carbon black content in the liquid colorants.
Therefore, we, the inventors, studied improvements in flowability of liquid colorants comprising an ordinary, low pH carbon black, having polar groups such as carboxylic groups or the like introduced thereinto by oxidation in a gaseous phase. However, we have found that although the gas phase oxidized ordinary carbon black can raise the jetness level to a certain degree, nevertheless an intended satisfiable jetness level cannot yet be reached and moreover practical problems occur, such as deterioration of polyester fibers.
In U.S. Pat. No. 3,992,218, there is disclosed a process for manufacturing colorants by flushing wherein furnace blacks having a pH value of at least 7 are wet-oxidized in an aqueous medium, mixed with a liquid vehicle, and then dehydrated to obtain colorants. It is shown in the above patent specification that when these colorants are used for inks, paints, and the like, it is preferred to use, as the liquid vehicle, toluene, xylene, mineral spirits and other hydrocarbon type solvents; butanol and higher alcohols; natural oil varnish, e.g., linseed oil varnish or tung oil varnish; synthetic resin varnish and the like, while when the colorants are used for polyvinyl chloride, it is preferred to use a plasticizer such as dioctyl phthalate, dibutyl phthalate or the like. However, from an aspect of the efficiency in removing the carbon black from aqueous media to liquid vehicles, the use of liquid vehicles, such as alcohols, e.g., butanol; plasticizers, e.g., phthalates; nonionic surface active agents, and the like, which have a reciprocal solubility in aqueous media, is not suitable for the flushing. Further, the use of solvents, such as alcohols, e.g., butanol; hydrocarbons, e.g., toluene, xylene and mineral spirits, and the like, as a liquid vehicle, is also not suitable for coloring polyester fibers. Thus, in the manufacture by flushing of the colorants for polyester fibers, there have been disadvantages such that employable liquid vehicles are limited in a very narrow range. Furthermore, the colorants manufactured by a process wherein a furnace black having a pH value of at least 7 is wet-oxidized in an aqueous medium and dried, without being subjected to the flushing, and then only mixed with a liquid vehicle, have had drawbacks such that a poor dispersibility of carbon black in polyester fibers dope-dyed therewith is liable to cause filament breakages.